1) one who elicits the truth by the use of the rack
1a) an inquisitor, torturer also used of a jailer doubtless because the business of torturing was also assigned to him
Part of Speech: noun masculine
Citing in TDNT: 1:561, 96
From G928; a torturer: - tormentor.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root βασανιστής; click on the second column to search for that grammatical form of the root βασανιστής; click on the third column to search for that word and grammatical form; click on the total to search for the root βασανιστής.